I don't know your machine, but on mine the interlock is the large access door. It's done so that you cannot open the cover while running, but it also checks for a closed door at startup due to head homing sequence. Yours may be similar in that it won't home the head unless it knows that the door is closed.
The front door has as security switch, indeed. It works ok. A lever switch for override the door switch is also included from factory. (It don´t look good from the safety point of view but, you know). There is also a presostatic switch on the air regulator that operates as an interlock on low pressure condition. It works fine too. Both generate a "1 STEP STOP" message when activated.
At this point all the sensors, switches and solenoid valves were checked. Their electrical signals and actions were phisically checked at the I/O cards level (Panadac 783-065 and 065A). Above mentioned signals were monitored from "I/O Monitor" function at the main console. Even I replaced the transport and head controllers by the respective brand new spares. I contacted the Panasonic thech support. A very skilled brazilian engineer came to my shop, but the visit was not fruitfull. It is a dead end. This unit is probably the oldest functional MPA machine in South America, maybe the only of the kind in Argentina. There are some units in Brazil, but these are newer and different versions than this, and the engineers are unfamiliarised.
I can move the axes XYUV just in short steps through the "MANUAL NC" function. The axis encoders seem to work; the readings of position follow the axis movements. However the actual position of the head has nothing to do with the readings at the display.
I changed the servo cards for head and transport by new ones. I did not checked the XY control card yet, since I was focused on the head's functions. It will be the next step.